Field of the Invention
The present invention relates to the transmission of movement between a driven part and a driving part, and more particularly to a coupling for coupling a driven part to a driving part by means of a safety pin.
Brief Discussion of the Related Art
Such a coupling generally comprises a male portion that is secured to one of the parts and received in a female portion that is secured to the other part. The transmission of force from the driving part to the driven part is performed by a safety pin extending perpendicularly to said direction through corresponding holes made in the male and female portions.
The safety pin is designed to have shear strength sufficient to transmit forces that are below a threshold: above the threshold, the safety pin breaks in order to protect the driving part and/or the driven part and/or elements that are connected to said parts from excessive force.
Once the safety pin has broken, if the movement of the driving part is not interrupted, the driving part must be capable of moving relative to the driven part without driving the driven part. The female portion and the male portion thus ensure relative guidance of the parts, and to this end they include guide surfaces that have the holes for receiving the safety pin passing therethrough.
That said, after the pin has broken, friction between the female portion and the male portion is usually very high, and can lead to the two portions seizing together. Movement thus continues to be transmitted, at least to some extent, despite the safety pin breaking.
A solution is to use a harder material for the male portion or to harden the material using a heat treatment. However, that increases the cost of the part considerably.